Method of peaking a power plant system



' Aug. 9, 1966 R. A. KANE ETAL 3,264,826

METHOD OF PEAKING A POWER PLANT SYSTEM Filed Aug. 8, 1963 2 Sheets-Sheet 1 FIGJ Z8 24 j v V (Z4 Z6 5&- {is 32 v 4 7 El 52 144 58 90 1966 R. A. KANE ETAL- 3,264,826

METHOD OF PEAKING A POWER PLANT SYSTEM Filed Aug. 8, 1963 2 Sheets-Sheet 2 FIC5.2 F'IG-3 United States Patent 3,264,826 METHQD 0F PEAKING A POWER PLANT SYSTEM Robert A. Kane, Hazardville, and Edward L. Kochey, Jr.,

Colehrook, Conn, assignors to Combustion Engineering, Inc, Windsor, Conn, a corporation of Delaware lFiled Aug. 8, 1963, Ser. No. 360,766 7 Claims. (Cl. 6073) This invention relates to vapor cycle power plant systems and particularly to a method of and means for peaking these plants.

The load demand on many plants and on public utilities in particular is such that, for short periods of time very high outputs are required. It is generally uneconomical to install highly efficient generating capacity to cover these peak load conditions. It has therefore been the practice of the industry to resort to a number of means to cover these peak demands.

Old equipment is sometimes retained and brought into service during these times. In some cases peaking capacity has been obtained through the purchase of diesel or gas turbine equipment.

The most frequently used peaking device has involved increasing the output of a single unit system by overfiring the steam generator and finding some way to put more steam through the turbine. Where the design of the system has been suificiently liberal this can be achieved to some extent by simply increasing the operating pressure of the steam generator. In many cases feedwater heaters are cut out thereby sending steam which had been extracted from the turbine through the low pressure stages of the turbine.

In each of these cases where the single unit system is peaked, additional heat input to the steam generator is required. The over-pressure peaking method requires the evaporation of more water and therefore more heat input. The method where feedwater heaters are cut out results in a lower feedwater temperature to the steam generator and therefore increased firing rate to maintain steam temperature. v

The design of the steam generator must necessarily be based on a maximum expected fuel burning capability. This imposes limits on furnace sizes to permit complete combustion before the gases enter the convection passes, and to permit operation with acceptable furnace slagging conditions. This also sets the size of the fans both as to capacity and 'head. The selection of the fuel burners, pulverizers, or oil pumps is obviously also set by this maximum heat input requirement.

In the design of a steam generator which is expected to operate under peaking conditions additional capacity must be built into the entire fuel and air systems. Even though this is required for only short term operation and even though efficiency is not particularly important at this time additional investment must be made in the original equipment to cover peak operation.

The use of old plant equipment is cumbersome since it requires frequent startup and shutdown of not only the steam generator, but also the turbine and electric generator. This imposes considerable thermal cycling on the equipment since the turbine must be warmed on each occasion. This also requires turbine warmup time and makes additional demand on manpower requirements.

The use of the diesel or gas turbine for peaking operation requires considerable additional investment.

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Modern high pressure power plants normally include an auxiliary low pressure boiler which is used during startup of the plant, which is generally not in operation when there is substantial load on the main steam generator. In accordance with the present invention this auxiliary low pressure boiler is employed and integrated into the system in a novel and simple way to obtain the desired peaking of the system.

It is an object of this invention to provide an improved method of and organization for peaking power plant systems.

It is a further object to achieve this peaking operation without increasing the heat input duty on the main steam generator.

Other and further objects of the invention will become apparent to those skilled in the art as the description proceeds.

With the aforementioned objects in view, the invention comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired as hereinafter more particularly set forth in the following detailed description of an illustrative embodiment, said embodiment being shown by the accompanying drawings wherein:

FIGURE 1 is a schematic diagram of a single reheat power plant system embodying the invention; and

FIGURES 2 and 3 are fragmentary portions of modified systems employing the double reheat cycle.

In FIGURE 1 water is pumped by condensate pump 2 from condenser 4 through low pressure piping 6 and low pressure heaters 8 into de-aerator 10 for oxygen removal. This low pressure water is then pumped by feed pump 12, which is driven by steam turbine 14 through feedwater heaters 16 and high pressure piping 18, entering steam generator 20 through feedwater valve 22. In the steam generator the water is vaporized and high temperature high pressure steam leaves through steam line 24, supplying high pressure turbine 26 through turbine throttle valve 28. Exhaust steam at a lower temperature and pressure passes through cold reheat line 30 and desuperheater 32, into reheater 34 where its temperature is increased. The steam then flows through hot reheat line 36 to intermediate pressure turbine 38, and then through low pressure turbine 40, returning to condenser 4 where the steam is condensed and the water starts another cycle. Turbines 26, 38, and 40 are arranged to form a tandem-compound turbine driving an electric generator (not shown).

Steam generator 20 is comprised of economizer 42, initial heating section 44 with recirculating pump 46 and recirculating line 48, and secondary heating section 50. Boiler throttle valve 52 is capable of shutting off flow between the primary and secondary heating sections. During startup valve 52 is closed, the flow passing through pipe 54 and boiler extraction valve 56 into flash tank 58. Water separated in this flash tank passes through water discharge valve 60 and pipe 62 returning to the condenser. Steam formed in the flash tank passes through pipe 64 and may be used for a number of purposes. It may pass through pipes 66 and 68 through control valve 70 to operate feed pump turbine 14. It may pass through pipes 66 and 72 through control valve 74 to supply steam to deaerator 10. The steam may pass through lines 64 and 76 through steam admission valve 7 8 thereby supplying steam to cool the superheater 5t) and to warm steam piping 24 and turbine 26; this steam may even be used to roll and synchronize the turbine-generator. Excess steam formed in the flash tank 58 is passed through pipe 80, valve 81, and desuperheater 82 to condenser 4.

Late in the startup valve 52 is opened and valves 56 and 78 are closed, so that the steam generator operates with all flow through valve 52 and the flash tank 58 is isolated.

The eflluent passing through valve 56 will not produce sufficient steam in flash tank 58 until a relatively high temperature has been reached. Auxiliary boiler 84 therefore supplies steam through stop check valve 86 thereby permitting steam to be used for feed pump turbine 14, de-aerator and warming and rolling turbine 26, before steam is available from the flash tank 58.

If it were not for this auxiliary boiler, turbine 14 which is selected in preference to an electric motor to improve the heat rate during normal operation would have to be supplemented by an electric motor drive for startup. Since no steam would be available during the early startup uncle-aerated feedwater would be introduced into the steam generator. Neither could the flow through the superheater, nor the turbine warming and rolling be started until the eflluent through valve 56 reaches a temperature which will produce a satisfactory amount of steam in flash tank 58. Using steam from the auxiliary boiler at this time through valve 78 produces flow in the tubes of superheater 50, thereby increasing the safety of operation and permits a saving of several hours in startup time by starting the turbine warmup process sooner.

When the power plant is operating at maximum continuous rating, flow is as shown by the heavy solid line, which was the first described flow path. In order to increase output of the plant to a peak rating, auxiliary boiler 84 is fired and steam is supplied through pipe 88 and control valve 90 to the cold reheat line 30. This permits increased output from the turbine without increasing the firing duty on the main steam generator.

FIGURES 2 and 3 are fragmentary portions of modified systems employing the double reheat cycle where steam passes through superpressure turbine 27 into cold reheat line 31. After passing through desuperheater 33 the steam is reheated in primary reheater 35 and passes through pipe 37 supplying high pressure turbine 91. Low temperature steam leaving this turbine passes through low pressure cold reheat line 93 and desuperheater 95. Steam is reheated in secondary pressure reheater 97 passing through low pressure hot reheat line 99 to intermediate pressure turbine 39 and then through low pressure turbine 41 condensing in condenser 4.

In FIGURE 2 the auxiliary steam supply for peaking the unit passe-s through pipe 88 and valve 90 into the low pressure reheat piping 93 where it joins with the exhaust steam from intermediate pressure turbine 91 passing on through reheater 97.

In FIGURE 3 auxiliary steam supplied for peaking the unit passes through pipe 88 and valve 90 into high pressure cold reheat piping 31 joining with exhaust steam from superpressure turbine 27 and passing through reheater 35.

While we have illustrated and described a preferred embodiment of our invention is to be understood that such is merely illustrative and not restrictive and that variations and modifications including supercritical as well as subcritical pressure operation may be made therein without departing from the spirit and scope of the invention. We therefore do not wish to be limited to the precise details set forth but desire to'avail ourselves of such changes as fall within the purview of our invention.

What we claim is:

1. A vapor plant system comprising in combination a main high-temperature high-pressure vapor generator, having first and second heating surfaces, and a valve for stopping flow of vapor from said first to said second heating surfaces, a flash tank, piping associated with said flash tank comprising, valved means connecting said first heating surface to said flash tank, valved means connecting said flash tank to said second heating surface, an auxiliary boiler the operating pressure of which is substantially lower than said main steam generator, having means connecting to said flash tank; a first turbine portion re ceiving vapor produced in said main vapor generator, reheater means receiving the exhaust from said first turbine portion, a second turbine portion receiving vapor from said reheat means; valved means for conveying vapor from said piping associated with said flash tank, and introducing it into the exhaust vapor from said first turbine portion, for conveyance to and through said second turbine portion.

2. A system as in claim 1 wherein the plant is operating on a double reheat cycle, said system including a superpressure turbine and a primary reheater, through which the vapor flows before entering said first turbine portion.

3. A vapor power plant system comprising in combination a main high-temperature, high-pressure vapor generator, having first and second heating surfaces, and a valve for stopping flow of vapor from said first to second heating surfaces; a first turbine portion receiving vapor produced in said main vapor generator, reheater means receiving the exhaust from said first turbine portion, a later turbine portion receiving vapor from said reheater means, a flash tank, piping associated with said flash tank comprising, a valved means connecting said first heating surface to said flash tank, and a valved means connecting said flash tank to said second heating surface; an auxiliary boiler having an operating pressure substantially lower than that of said main steam generator, and having an operating temperature substantially lower than that of the steam delivered to said turbine portion; said auxiliary boiler having means connecting to said flash tank, and valved means for conveying vapor from said piping associated with said flash tank and introducing it into the exhaust vapor from said first turbine portion, for conveyance to and through said reheating means and through later turbine portion.

4. A vapor power plant system comprising in combination a main high-temperature, high-pressure vapor generator, having first and second heating surfaces, a valve for stopping flow of vapor from said first to second heating surfaces; a first turbine portion receiving vapor produced in main vapor generator, reheater means receiving the exhaust from said first turbine portion, a later turbine portion receiving vapor from said reheater means, a flash tank, a valved means connecting said first heating surface to said flash tank, a valved means connecting said flash tank to said second heating surface; an auxiliary boiler having an operating pressure substantially lower than that of said main steam generator, and having an operating temperature substantially lower than that of the steam delivered to said later turbine portion, said auxiliary boiler having valved means connecting to said flash tank; valved means for conveying vapor from said auxiliary boiler and introducing it into the exhaust vapor from said first turbine portion, for conveyance to and through said reheating means and through said later turbine portion.

5. In a power plant system comprising a main vapor generator having a primary heating section and a secondary heating section, with a boiler throttle valve means between them; a multi-stage turbine having a first portion and a second portion; an auxiliary boiler associated therewith: the method of operation comprising, starting up the power plant system by closing said boiler throttle valve, firing said main vapor generator, and supplying vapor from said auxiliary boiler through said secondary heating section of the main vapor generator; thereafter opening said boiler throttle valve, delivering vapor through said boiler throttle valve from said primary heating section to said secondary section, and ceasing delivery of vapor from said auxiliary boiler; providing a predetermined output for said power plant system by operating the main vapor generator at maximum capacity delivering vapor therefrom through said first turbine portion and then through said second turbine portion; and in creasing output above said predetermined output by supplying vapor from said auxiliary boiler to said second turbine portion, while maintaining the fiow of vapor from said main vapor generator to said turbine 6. A method as in claim 5, where reheating means are interspersed between said first and second turbine portions and where vapor from said auxiliary boiler is passed through said reheating means, along with vapor leaving said first turbine portion, thereby increasing the tempenature of the vapor to the desired value before delivery to said second turbine portion.

by the auxiliary boiler is regulated to meet the peak load required.

References Cited by the Examiner UNITED STATES PATENTS EDGAR W. GEOGHEGAN, Primary Examiner.

7. A method as in claim 5 where the vapor supplied 15 ROBERT BUNEVICH, Examiner- 

1. A VAPOR PLANT SYSTEM COMPRISING IN COMBINATION A MAIN HIGH-TEMPERATURE HIGH-PRESSURE VAPOR GENERATOR, HAVING FIRST AND SECOND HEATING SURFACES, AND A VALVE FOR STOPPING FLOW OF VAPOR FROM SAID FIRST TO SAID SECOND HEATING SURFACES, A FLASH TANK, PIPING ASSOCIATED WITH SAID FLASH TANK COMPRISING, VALVED MEANS CONNECTING SAID FIRST HEATING SURFACE TO SAID FLASH TANK, VALVED MEANS CONNECTING SAID FLASH TANK TO SAID SECOND HEATING SURFACE, AN AUXILIARY BOILER THE OPERATING PRESSURE OF WHICH IS SUBSTANTIALLY LOWER THAN SAID MAIN STEAM GENERATOR, HAVING MEANS CONNECTING TO SAID FLASH TANK; A FIRST TURBINE PORTION RE CEIVING VAPOR PRODUCED IN SAID MAIN VAPOR GENERATOR, REHEATER MEANS RECEIVING THE EXHAUST FROM SAID FIRST TURBINE PORTION, A SECOND TURBINE PORTION RECEIVING VAPOR FROM SAID REHEAT MEANS; VALVED MEANS FOR CONVEYING VAPOR FROM SAID PIPING ASSOCIATED WITH SAID FLASH TANK, AND INTRODUCING IT INTO THE EXHAUST VAPOR FROM SAID FIRST TURBINE PORTION FOR CONVEYANCE TO AND THROUGH SAID SECOND TURBINE PORTION. 